In recent years, nanotechnology has made considerable strides recently, and in particular, a molecular structure such as a carbon nanotube is a stable material having superior properties such as high thermal conductivity, high electrical conductivity and high mechanical strength, so it is expected that the molecular structure is applied to a wide range of uses such as transistors, memories and field electron emission devices.
For example, as one of the uses of the carbon nanotube, it is known that the carbon nanotube is suitable to achieve cold cathode field electron emission (hereinafter referred to as “field electron emission”) (for example, refer to Yahachi Saito, Journal of The Surface Science Society of Japan, 1998, Vol. 19, No. 10, p. 680-686). The field electron emission is a phenomenon that when an electric field larger than a predetermined threshold is applied to a metal or a semiconductor placed in a vacuum, electrons pass through an energy barrier near the surface of the metal or the semiconductor by a quantum tunneling effect, thereby electrons are emitted in a vacuum even at room temperature.
An FED (Field Emission Display) which uses the principle of the field electron emission to display an image has characteristics such as high intensity, low power consumption and a low profile, and the FED has been developed as an alternative display unit to a conventional cathode ray tube (CRT) (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2002-203473 and 2000-67736). As a typical structure of the FED, a cathode panel in which a cathode emitting electrons is formed, and a anode panel in which an anode coated with a phosphor layer emitting light through being excited by collision of emitted electrons are combined as one unit so as to face each other, and the interior of the FED is in a high vacuum state. However, in the structure, it is difficult to dispose the cathode panel and the anode panel at a close distance, so it is necessary to apply a high voltage between the cathode panel and the anode panel. Therefore, an extraction electrode (gate electrode) is disposed between the cathode panel and the anode panel so as to bring the cathode and the extraction electrode closer, and a low voltage is applied between the electrodes to cause field electron emission.
FIG. 75 shows a sectional view of a configuration example of such a conventional FED. In the example, as a kind of the structure of a cathode, a structure called a Spindt (derived from a personal name) type with a conical shape is shown (for example, refer to C. A. Spindt and other three, Journal of Applied Physics, (U.S.), 1976, Vol. 47, p. 5248-5263, and Japanese Unexamined Patent Application Publication No. 2002-203473).
The FED includes a cathode panel 1100 and an anode panel 1200 facing the cathode panel 1100. The cathode panel 1100 includes a substrate 1120 on which a cathode electrode 1110 is formed and an extraction electrode 1140 facing the cathode electrode 1110 with an insulating film 1130 in between. A plurality of cathode electrodes 1110 and a plurality of extraction electrodes 1140 are formed, and each extraction electrode 1140 is disposed orthogonally opposite to the cathode electrodes 1110. On the substrate 1120, a plurality of cathodes 1150 are disposed on surfaces of the cathode electrodes 1110 on a side facing the extraction electrodes 1140.
In each extraction electrode 1140, a plurality of aperture portions 1160 with as large a size as electrons e− emitted from the cathodes 1150 can pass through are disposed corresponding to each cathode 1150. Moreover, a scan driver (not shown) which circularly applies a scanning voltage to each extraction electrode 1140 is electrically connected to each extraction electrode 1140. On the other hand, a data driver (not shown) which selectively applies a voltage to each cathode electrode 1110 according to an image signal is electrically connected to each cathode electrode 1110.
Each cathode 1150 is disposed in a matrix form corresponding to a position where the extraction electrode 1140 and the cathode electrode 1110 cross each other, and the bottom surface of each cathode 1150 is electrically connected to a corresponding cathode electrode 1110. The cathode 1150 emits electrons from a tip portion by a tunneling effect through selectively applying a predetermined electric field. Further, in a typical FED, a group of a predetermined number (for example, 1000) of cathodes 1150 corresponds to 1 pixel.
The anode panel 1200 includes a transparent substrate 1210 which is made of a glass material or the like and is optically transparent, and an anode electrode 1220 which is disposed on a surface of the transparent substrate 1210 on a side facing the cathode panel 1100. A plurality of anode electrodes 1220 are formed corresponding to the cathode electrodes 1110. Moreover, a phosphor which emits light according to the injection of electrons e−, is applied to surfaces of the anode electrodes 1220 on a side closer to the transparent substrate 1210 so as to form a phosphor film 1230. Further, the anode electrodes 1220 can be made of a transparent conductive material such as ITO (Indium-Tin Oxide), and the phosphor film 1230 can be formed on surfaces of the anode electrodes 1220 on a side closer to the cathode panel 1100.
In the FED with such a structure, when a voltage is selectively applied between the extraction electrode 1140 and the cathode electrode 1110, field electron emission occurs in the cathode 1150 in an intersection point of the extraction electrode 1140 and the cathode electrode 1110, electrons e− are emitted toward the anode electrode 1220. The electrons e− emitted from the cathode 1150 pass through a fine hole (not shown) disposed in the anode electrode 1220 to come into collision with the phosphor film 1230, thereby the phosphor emits light. A desired image is displayed by the light emission from the phosphor.
In the FED, field electron emission occurs by a lower voltage, so various attempts to locally increase an electric field strength through making a tip of the cathode sharp-pointed have been made, and the carbon nanotube is increasingly used in such attempts (for example, refer to Yahachi Saito, Journal of The Surface Science Society of Japan, 1998, Vol. 19, No. 10, p. 680-686). For example, an FED using a single-wall carbon nanotube grown on a tip of a silicon (Si) chip by a thermal CVD (Chemical Vapor Deposition) method as a cathode has been proposed (for example, refer to 49th Extended Abstracts, Japan Society of Applied Physics and Related Societies, 29p-k-7). Moreover, there is a report that after a silicon emitter is formed by a conventional method, a film made of a metal catalyst for forming a carbon nanotube is formed, and a catalyst film on a grid electrode is removed by an etch-back method, and a carbon nanotube is grown only in a tip portion of the emitter by a thermal CVD method (refer to an article in the Nikkan Kogyo shimbun, Apr. 11, 2002, “electron emission from field emitter of CNT at 4V low voltage”).
In such an application field, the carbon nanotube is not used alone, but a carbon nanotube structure including a plurality of carbon nanotubes is used. As a method of manufacturing a carbon nanotube structure, conventional semiconductor techniques such as photolithography and CVD (Chemical Vapor Deposition) are used. Moreover, a technique that a foreign material is included in a carbon nanotube has been disclosed (for example, refer to Masafumi Ata, and other three, Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.), 1995, Vol. 34, p. 4207-4212, and Masafumi Ata and other two, Advanced Materials, (Germany), 1995, Vol. 7, p. 286-289).
Moreover, as another technique related to the invention, there are a magnetic recording device and a magnetic recording apparatus. Their principle is that a magnetic material is magnetized, and by coercivity, a magnetization direction corresponds to 1 or 0, or the analog quantity of a signal which records the degree of magnetization when the magnetic material is magnetized. In this case, in-plane magnetization in a horizontal direction to a recording surface and a perpendicular magnetization perpendicular to the recording surface are both in practical use. In recent years, a further improvement in recording density is in demand, and conventionally, the length of magnetization is reduced to improve the recording density. To the best of the knowledge of the inventors, an attempt to apply a carbon nanotube to such a magnetic recording technique has not been disclosed yet.
In order to achieve an FED or the like using a carbon nanotube structure, a technique that a fine pattern of a catalyst made of a transition metal or the like is formed so as to regularly align carbon nanotubes with a fine spacing is necessary. However, conventionally, photolithography is the only technique which can achieve mass productivity to some extent. Photolithography is a technique basically suitable for forming a two-dimensional structure, so photolithography is not suitable for forming a three-dimensional structure such as the carbon nanotube structure.
Moreover, in order to form a fine pattern of a metal catalyst by photolithography, there is no way but to reduce the wavelength of an energy beam, and in the present technique, it is difficult to further reduce the wavelength. Therefore, in the case where the pattern of a transition metal or the like is formed by photolithography, a dimension of the transition metal pattern and a spacing between patterns are determined by the wavelength of the energy beam, and in the present technique, the dimension cannot be reduced to 0.05 μm (50 nm) or less and a spacing (pitch) between patterns cannot be reduced to 100 nm or less. In other words, there is a problem that the conventional technique has a limit of forming a finer pattern of a metal catalyst or the like.
Further, in a cathode using a conventional carbon nanotube, a large number of carbon nanotubes are closely disposed, so there is a problem that an electric field strength on the surface of each carbon nanotube pronouncedly declines. Therefore, in order to increase the electric field strength on the surface of the carbon nanotube, it is necessary to apply a high voltage between a cathode electrode and an extraction electrode or an anode electrode, so it is difficult to lower the voltage.
In addition, conventionally, the shapes and growth directions of a large number of carbon nanotubes constituting the cathode are not uniform, so the amount of emitted electrons are not uniform, thereby there is a problem that variations in intensity occurs.